Conventionally in general terms, a thin groove called a defense groove that continues in a straight line in the tread circumferential direction is provided in a shoulder rib, and by this thin groove, preventing the progress of eccentric wear over the entire shoulder rib, and eventually, the spreading of that eccentric wear to the rib on the side of the tread center is prevented from occurring.
In addition to the thin groove that has this function, there is also known one that moreover provides an annular groove that is continuous in the circumferential direction in a groove wall of this thin groove that is on the tread equatorial surface side to be contiguous to the groove bottom (for example, refer to Patent Document 1, FIG. 6(b)).
In a pneumatic tire that also provides an annular groove at the groove bottom of the thin groove in this way, it is of course possible to confine eccentric wear to the tread edge side portion from the thin groove, and in addition, due to eccentric wear that is confined to the tread edge side portion, when the tire subsequently undergoes load rolling, even in the case of the remainder of the shoulder rib (the tread center side portion that does not receive the eccentric wear) deforming greatly to the inner circumferential side in the tire radius direction compared to the tread edge side portion, it is possible to relieve the concentration of strain at the groove bottom of the thin groove by the annular groove, and thereby the advantage is obtained of being able to suppress the occurrence of cracking or the like at the groove bottom of the thin groove.    [Patent Document 1] Japanese Unexamined Patent Application, First Publication No. H11-301214